Bishop Richard Malone on Wednesday assigned the Rev. Robert Vaillancourt to serve as temporary administrator at St. John Vianney Parish after the Rev. James Nadeau took a voluntary leave of absence pending an investigation by the state attorney general’s office.

Neither the diocese nor the attorney general has disclosed the reason for the investigation.

The 58-year-old Vaillancourt was born in Lewiston and was ordained in 1982.